The driveside threads are presumably the actual body of the cartridge? That needs to be done up fully until it contacts the frame (no need to go mad with high torque, though). Then fit the NDS cup fairly firmly, and not too firmly at all if it's plastic. In steel frames I lather the threads in copperslip first, not tried loctite there...

It's because you tightened up the nds first. You should tighten the drive side first then the nds. It's the drive side that tightens against the frame the. The nds tightens against the end of the bb shell. So what's happening is the bb is moving in the frame because its not actually tight. Undo the nds, tighten the drive side and retighten the non drive side. If you no already damaged it (too much) it should be fine.